STUDENTS at one of America's most prestigious schools were abused by paedophile teachers for more than three decades but prosecutors are unable to file charges because the crimes happened too long ago, officials in New York say.

The Bronx District Attorney's Office said in a statement police had uncovered evidence of systemic abuse of pupils at the famous Horace Mann School, spanning a 34-year period from from 1962 to 1996.

However, no charges would be filed because of New York State's statute of limitations laws.

Horace Mann, seen as offering the best education money can buy with an annual tuition of almost $US40,000 (about $A39,000), was the subject of an expose in the New York Times Magazine last June in which a former student alleged there had been numerous cases of sexual contact between students and teachers during the 1970s, 80s and 90s.

After the publication of the article, a number of alleged victims came forward saying they had also suffered sexual abuse at the school.

Prosecutors said today that a police investigation uncovered a "systemic pattern of alleged abuse" which exceeded the crimes detailed by the New York Times.

"In total, we received direct information regarding at least 12 separate alleged abusers," the statement from the Bronx District Attorney's office read.

"The reported abuse ranges from what may be characterised as inappropriate behaviour to child endangerment, actual instances of sexual contact, sexual intercourse and criminal sexual acts," according to the prosecutors' statement, which said the abuse went on from 1962 to 1996.

But because so much time has elapsed, prosecutors said they were unable to file charges in the cases.

In most of the cases, the statute of limitation for paedophilia-related charges was five years or less, they said.

Horace Mann was founded in 1887 and offers a rigorous classical education, with students from preschoolers to high school.

A large percentage of graduates go on to study at Harvard, Princeton, Yale and other Ivy League schools.